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United States Patent |
6,138,810
|
Fujii
,   et al.
|
October 31, 2000
|
Method for controlling a hydraulic valve of an automatic transmission
Abstract
A method for controlling operation of a hydraulic valve having a magnet
fixed to a displaceable spool, a sensor producing a signal responsive to
the sensed intensity of a field produced by the magnet representing the
position of the spool in the valve spool, the method comprising producing
from the signal a time series record of the position of the spool;
determining the desired position of the spool, producing a error signal
from the difference between actual and desired spool position, determining
a compensated correction error, producing a commanded control pressure
signal to change the magnitude of control pressure supplied to the valve,
and changing the position of the spool in response to the control pressure
signal.
Inventors:
|
Fujii; Yuji (Ann Arbor, MI);
McCallum; James William Loch (Ann Arbor, MI);
Kraska; Marvin Paul (Dearborn, MI)
|
Assignee:
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Ford Global Technologies, Inc. (Dearborn, MI)
|
Appl. No.:
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368218 |
Filed:
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August 4, 1999 |
Current U.S. Class: |
192/85R; 192/109F |
Intern'l Class: |
F16D 025/00 |
Field of Search: |
192/85 R,109 F
251/31,65,129.06
|
References Cited
U.S. Patent Documents
4116321 | Sep., 1978 | Miller | 192/109.
|
4617968 | Oct., 1986 | Hendrixon.
| |
4942787 | Jul., 1990 | Aoki et al. | 192/109.
|
4962831 | Oct., 1990 | Dundas.
| |
5002090 | Mar., 1991 | Ichikawa et al.
| |
5240041 | Aug., 1993 | Garnjost.
| |
5244002 | Sep., 1993 | Frederick.
| |
5722459 | Mar., 1998 | Kim et al.
| |
5787915 | Aug., 1998 | Byers et al.
| |
5826616 | Oct., 1998 | Golden.
| |
5957260 | Sep., 1999 | Kunii | 192/85.
|
Primary Examiner: Lorence; Richard M.
Assistant Examiner: Rodriguez; Saul J.
Attorney, Agent or Firm: McKenzie; Frank G.
Claims
We claim:
1. A method for controlling operation of an automatic transmission having a
hydraulic valve that controls operation of a friction element, having a
magnet fixed to a displaceable valve spool, a sensor producing a signal
responsive to the sensed intensity of a field produced by the magnet
representing the position of the spool in the valve, the method comprising
the steps of:
producing from the signal a time series record of the position of the
spool;
determining the desired spool position;
determining a spool position error from the current spool position and
desired spool position;
determining a compensated spool position from said spool position error;
determining a current commanded control pressure from said compensated
spool position and a prior commanded control pressure;
changing the magnitude of control pressure applied to the valve in response
to said current commanded control pressure; and
changing the position of the spool in response to the current control
pressure.
2. The method of claim 1, further comprising:
determining from said time series record of the position of the spool, the
current spool velocity and acceleration;
continually comparing predetermined magnitudes of spool velocity
corresponding to a valve stiction event to said current spool velocity;
continually comparing of spool acceleration corresponding to a valve
stiction event to current spool acceleration; and
producing a warning indicating the presence of a valve stiction event
whenever said current spool velocity or current spool acceleration exceeds
the corresponding predetermined magnitude.
3. The method of claim 1, further comprising:
determining from said time series record of the position of the spool, the
current spool velocity and acceleration;
continually comparing predetermined magnitudes of spool velocity
corresponding to a valve oscillation event to said current spool velocity;
continually comparing of spool acceleration corresponding to a valve
oscillation event to current spool acceleration; and
producing a warning indicating the presence of a valve oscillation event
whenever said current spool velocity or current spool acceleration exceeds
the corresponding predetermined magnitude.
4. A method for controlling operation of an automatic transmission having a
hydraulic valve that controls a first period during which a friction
element is being filled with fluid and regulates fluid pressure in the
friction element, having a magnet fixed to a displaceable valve spool, a
sensor producing a signal responsive to the sensed intensity of a field
produced by the magnet representing the position of the spool in the
valve, the method comprising the steps of:
producing from the signal a time series record of the position of the
spool;
following a command to engage the friction element, continually comparing
the length of said first period and the desired length of said period;
determining a first desired spool position corresponding to said period;
determining a spool position error from a current spool position and a
first desired spool position;
determining a compensated spool position from said spool position error;
determining a current commanded control pressure from said compensated
spool position and a prior commanded control pressure;
changing the magnitude of control pressure applied to the valve in response
to said current commanded control pressure; and
changing the position of the spool in response to the current control
pressure.
5. The method of claim 4, further comprising:
following expiration of said period, determining magnitudes of second
desired spool position during a second period in which the pressure in the
friction element is being regulated;
determining a spool position error from a current spool position and a
second desired spool position;
determining a compensated spool position from said spool position error;
determining a current commanded control pressure from said compensated
spool position and a prior commanded control pressure;
changing the magnitude of control pressure applied to the valve in response
to said current commanded control pressure; and
changing the position of the spool in response to the current control
pressure resulting from the current commanded control pressure.
6. The method of claim 4, further comprising:
determining from said time series record of the position of the spool, the
current spool velocity and acceleration;
continually comparing predetermined magnitudes of spool velocity
corresponding to a valve stiction event to said current spool velocity;
continually comparing of spool acceleration corresponding to a valve
stiction event to current spool acceleration; and
producing a warning indicating the presence of a valve stiction event
whenever said current spool velocity or current spool acceleration exceeds
the corresponding predetermined magnitude.
7. The method of claim 4, further comprising:
determining from said time series record of the position of the spool, the
current spool velocity and acceleration;
continually comparing predetermined magnitudes of spool velocity
corresponding to a valve oscillation event to said current spool velocity;
continually comparing of spool acceleration corresponding to a valve
oscillation event to current spool acceleration; and
producing a warning indicating the presence of a valve oscillation event
whenever said current spool velocity or current spool acceleration exceeds
the corresponding predetermined magnitude.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to the field of hydraulic systems, more particularly
it pertains to control of valves used in such systems to operate an
automatic transmission for motor vehicles.
2. Description of the Prior Art
A gear ratio change in a conventional automatic transmission is
accomplished by applying or releasing a friction element (a brake or
clutch) that changes the speed and torque relationship by means of
planetary gearsets. Friction elements are hydraulically controlled by
pressure regulator valves and flow regulator (shift control) valves.
Pressure regulator valves control hydraulic pressure, which determines
friction element torque capacity. Flow regulator valves, which control a
flow rate of pressurized oil into a friction element, determines the time
rate of friction element torque capacity change.
A continuously variable transmission (CVT) uses a special variator to
change the speed and torque relationship continuously. Variators are
hydraulically controlled by pressure regulator valves and flow regulator
valves. Pressure regulator valves control hydraulic pressure, which
determines the variator torque capacity. Flow regulator valves, which
control the flow rate of fluid into variator pistons, determines the rate
of speed ratio change. In both conventional automatic transmissions and
CVTs, precise control of the valve motion is vital to providing and
maintaining good shift quality and durability.
Conventional automatic transmission systems do not monitor motion of
pressure and flow regulator valves. oscillatory motion of pressure
regulator valves can cause undesirable hydraulic pressure oscillation,
which can degrade shift quality. Also, it can potentially emit audible
noise. Conventional flow regulator valves may include a fixed flow control
geometry called "notches". This passive method may not perform optimally
in all situations. Unit-to-unit variations and component degradation of
pressure and flow regulator valves over the life of the transmission may
cause shift quality degradation with the conventional approach.
SUMMARY OF THE INVENTION
Valve position is determined by a combination including magnet fixed to a
valve spool and a sensor that produces a signal representing the spool
position derived from the intensity of the magnetic field produced by
magnet on the spool. Valve velocity and acceleration are computed from a
time series of valve spool position signals. By this method, a signal is
available representing the full range of valve position within the bore.
When the technique method is applied to a pressure regulator valve, it
provides a signal used to reduce hydraulic pressure oscillation.
Valve oscillation which causes pressure oscillation can be actively
controlled through feedback of valve position and velocity. When it is
applied to a flow regulator valve, it overcomes the uncertainty of flow
control. The valve opening, which determines oil flow rate into the
friction element piston or CVT variator pistons, can be actively
controlled through feedback of valve position and velocity.
Motion characteristics of both pressure and flow regulator valves are
affected by unit-unit variation as well as operating conditions such as
oil temperature. Component wear and degradation of lubrication fluid can
affect the valve motion over the life of the system. The feedback control
allows the automatic transmission system to maintain a good shift quality
over the life of the system. In addition, monitoring valve motion over the
life of the transmission gives an indication of potential valve
malfunction due to excessive material wear or debris particles in the
transmission fluid.
In realizing these objects and advantages, in a an automatic transmission
having a hydraulic valve that controls operation of a friction element a
magnet fixed to a displaceable valve spool, a sensor producing a signal
responsive to the sensed intensity of a field produced by the magnet
representing the position of the spool in the valve, the method of this
invention includes the steps of producing from the signal a time series
record of the position of the spool; determining the desired spool
position; determining a spool position error from the current spool
position and desired spool position; determining a compensated spool
position from said spool position error; determining a current commanded
control pressure from said compensated spool position and a prior
commanded control pressure; changing the magnitude of control pressure
applied to the valve in response to said current commanded control
pressure; and changing the position of the spool in response to the
current control pressure resulting from the current commanded control
pressure.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a cross section through a valve body showing a pressure control
valve located in a bore for supplying hydraulic fluid to a friction
element of an automatic transmission.
FIG. 2 is a cross section through a valve body showing a flow regulator
valve located in a bore for supplying fluid to a friction element of an
automatic transmission.
FIGS. 3 and 4 show test data for a main pressure regulator valve relating
hydraulic line pressure and valve spool position as measured according to
this invention.
FIG. 5 is a graph of valve spool position vs. time or control pressure.
Traces of spool velocity and acceleration during normal operation,
oscillation and stiction events are shown.
FIG. 6 is a schematic diagram of a system for producing a control pressure
signal that controls the position of a valve spool.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring first to FIG. 1, a sensor 10, an inexpensive semiconductor linear
magnetic field strength sensor of either the Hall-effect or GMR type,
senses the strength of a magnetic field 11 through a magnetically
permeable valve body 12, the magnetic field being generated by a permanent
magnet 13, located in a pocket or recess at the end of the valve spool 14
adjacent the sensor 10.
Preferably the valve body is of aluminum alloy, the sensor is a linear
Hall-effect sensor available commercially as Part Number 3515L from
Allegro MicroSystems, Inc. of Worcester, Mass., and the magnet is a
Neodymium Iron Boron (NdFeB) and Samarium (SmCo) magnet available
commercially from Magnet Sales & Manufacturing Inc. of Culver City, Calif.
The spool is held in a closed position by the total control force applied
to the spool, the sum of the force of return spring 16 and the hydraulic
pressure force acting on control land 20 due to control pressure supplied
to the valve bore through port 18. When a reaction force caused by line
pressure in port 22 equals or exceeds the total control force, the valve
starts moving leftward from its closed position where the right-hand end
of the spool abuts the valve body. Valve displacement is directly related
to the width of a fluid flow path opening between the control edge 24 of
land 20 and the edge of exhaust port 28. As exhaust port 28 opens, line
pressure in port 22 reduces to balance the total control force. Line
pressure is controlled by varying the control pressure.
The magnitude of the magnetic field strength sensed by sensor 10 varies
approximately in proportion to the square of valve displacement. The
signal produced by the sensor 10 is compatible with analog input circuits
in controllers and can be digitized to produce a digital signal indicative
of valve position. By proper interpretation of this signal, a control
program can determine the exact time when the valve opens and the degree
to which it opens. Further interpretation of this signal can show the
effects of wear, valve sticking, or presence of debris particles.
FIG. 2 shows the elements of a flow regulator valve adapted for use with
this invention, the valve being partially displaced from the closed
position. Sensor 10 and magnet 13 are attached in the same way as
described for the pressure regulator valve of FIG. 1. Spool 30 is held in
a closed position by return spring 32. When the reaction force caused by
control pressure supplied through port 34 equals or exceeds the force of
spring 32, the valve spool begins to move leftward from the closed
position and uncovers a fluid flow path opening between the control edge
of the land and the right-hand edge of port 38. Valve displacement is
directly related to the width of the opening and controls the flow rate of
pressurized fluid, supplied to the valve through port 36 and delivered
through port 34 to an apply piston of a friction element, such as a clutch
or brake of a step-change automatic transmission, or to a variator piston
of a continuously variable transmission CVT. The valve position is
determined in the same way as described above for the pressure regulator
valve.
FIGS. 3 and 4 show test data representing line pressure and valve position,
determined by the technique of this invention, for a pressure regulator
valve. As FIG. 3 shows, main line pressure is regulated at about a
magnitude of 160 psi while oil flow, represented by the
constant-displacement-pump speed, increases. Control pressure is kept
constant at about 40 psi. The valve is initially closed 40 at low pump
speed. As pump speed increases, oil flow pressurizes the valve body and
line pressure increases 42. When line pressure reaches approximately 125
psi 44, the valve spool begins to move leftward from the closed position.
This movement opens a flow path to exhaust port 28, thereby regulating
line pressure. As the pump speed continues to increase, the valve opens
further at 46 to exhaust port 28, thereby maintaining line pressure at
about 160 psi.
As FIG. 4 shows, control pressure varies from 5 to 70 psi to regulate line
pressure. Flow into the valve body is kept constant by constant pump
speed. The spool position data, derived from the magnitude of the magnetic
field as explained below, shows the relation between valve position 48 and
line pressure 47. As control pressure increases, the control force
increases and pushes the valve toward the closed position and restricts
exhaust flow, which causes an increase in line pressure.
A continuous analog voltage representing the position of spool 14 or 30 in
the valve bore is produced by sensor 10 in response to the magnitude at
the sensor of the magnetic field produced by magnet 13. That voltage
signal is periodically sampled and digitized by a powertrain control
module. The resulting signal, after being transformed through use of a
table lookup, comprises a time series history of valve position
valve position X(k)=F(analog-to-digital v(t)), (1)
wherein F() is implemented as a table lookup.
Given the signal described in equation (1), the powertrain control module
approximates the velocity and acceleration of the valve spool by numeric
differentiation of the time series:
valve velocity Xdot(k)=(X(k)-X(k-1))/T (2)
valve acceleration Xddot(k)=(Xdot(k)-Xdot(k-1))/T, (3)
wherein T is the controller sampling time.
Using the signals described in equations (2) and (3), the powertrain
control module determines when a pressure regulating valve or flow control
valve is sticking or oscillating by continuously comparing the current
valve spool velocity Xdot(k) and current valve spool acceleration Xddot(k)
against a predetermined profile or trace of valve velocity and
acceleration, preferably stored in an electronic database accessible to a
microprocessor of the control module.
For example, reference traces of valve spool velocity and acceleration
during normal valve operation are represented in FIG. 5 at 50 and 52,
respectively. A reference magnitude 54 associated with normal valve
operation is stored in a database for comparison to corresponding data
derived from current operation. If the valve sticks, traces of
displacement, velocity and acceleration are zero. However, reference
traces of valve spool velocity and acceleration at the end of a valve
stiction event represented in FIG. 5 at 56 and 58, respectively, show
abrupt changes in spool velocity and acceleration. Reference traces of
valve spool velocity and acceleration during a valve oscillation event are
represented in FIG. 5 at 60 and 62, respectively. A reference magnitude 64
associated with the oscillation event is stored in a database for
comparison to corresponding data derived from current operation. Whenever
a reference magnitude corresponding to these events is reached or exceeded
by current magnitudes, a warning indication perceptible to the vehicle
operator is produced.
FIG. 8 shows schematically a system for controlling a valve using the
signal produced by the valves described above with reference to FIGS. 1
and 2. The voltage signal produced by sensor 10 is converted by look-up
table 70 to a digital count carried on line 72 representing the current
valve position relative to a reference position.
Using the valve spool position signal described with reference to equation
(1), the powertrain control system determines exactly when a flow control
valve begins to admit fluid to the friction element cylinder or vent fluid
by comparing valve position X(k) to a stored threshold position. If the
time to fill the cylinder of the friction element with fluid is not as
desired, the performance of a pressure control valve can be improved by
modulating the control pressure with closed loop feedback of the pressure
control valve position X(k), especially while the friction element is
being filled with fluid and being vented.
For example, as represented in FIG. 8, the control determines the desired
spool position from a predetermined schedule of position and time
corresponding to the period during which the friction element piston is
being filled with fluid and the period thereafter during which fluid
pressure in the friction element is regulated. During the fill process,
the control pressure is increased until the desired valve spool position
XDES is attained. XDES is carried on line 74 to junction 76. As the
cylinder of the friction element fills, control pressure reverts to the
desired regulation value. This change of valve position results in
response to an electronic command signal PRESX applied to a
solenoid-operated valve that changes the magnitude of control pressure.
The signals on lines 72 and 74 are combined at summing junction 76, where
an error signal XERR is produced and carried on line 78 to compensation
gain or amplification gain 80. Next an incremental PID compensator
produces corresponding proportional, differential and integral
compensation to junction 82, which produces a correction error XPID
carried on line 84. The command signal produced at the immediately prior
sampling interval PRESX(-1) is combined with XPID at junction 86, which
produces the control pressure command signal PRESX, carried on line 88 to
the solenoid, the signal producing the commanded magnitude of control
pressure in response to PRESX. At the start of a gear ratio change that
requires filling and pressurizing the cylinder of an on-coming friction
element for which there is no prior commanded control pressure, preferably
PRESX(-1) should represent the commanded control pressure corresponding to
the desired valve position. In this way the valve position changes in
response to the commanded control pressure to produce the desired
position.
The sensing method of this invention is noninvasive, easily packaged, and
takes advantage of magnetic permeability of typical automatic transmission
hydraulic valve body to sense internal valve movement from outside the
valve body. A direct relationship of sensor signal to valve oscillation
provides information regarding hydraulic pressure oscillation, and of oil
flow rate into a friction element piston or a CVT variator piston. Direct
indication of the valve motion provides improved hydraulic pressure and
flow management for improved shift quality. Valve motion provides
information to the automatic transmission control strategy applicable to
failure mode detection and management.
Although the form of the invention shown and described here constitutes the
preferred embodiment of the invention, it is not intended to illustrate
all possible forms of the invention. Words used here are words of
description rather than of limitation. Various changes in the form of the
invention may be made without departing from the spirit and scope of the
invention as disclosed.
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